Go Graphite if you prefer a glossy, dark finish. And natural Titanium if you prefer a lighter, more matte, brushed finish that also has a bit of shine in the sun. Titanium is also lighter on the wrist, making it more comfortable. However, Stainless Steel in my opinion has the edge in looking more distinct from the entry-level aluminium.
I’d be paying more attention to the fact that one is a Series 5 and one is a Series 6, its not an equal comparison truly then - Series 6 has faster charging, faster processor, blood oxygen monitoring, and a brighter 2nd gen AOD. Series 5 has the same chip as 2018’s Series 4.
In my opinion, you should also try both of the watches you have with your existing band collection if you have any and see which watch matches more with what you have.
BUT, if this were a comparison between Series 5 Ceramic and Series 6 Graphite, I’d probably point to Ceramic if it were in price range, because unlike the Titanium, Ceramic isn’t available for Series 6 and in fact theoretically may never return in a future Apple Watch so you’d really have that edge of exclusivity of a recent-gen special edition Watch